Mammalian FUBP-family proteins play roles in both RNA processing and transcription, by binding single stranded nucleic acids via their KH domains. In Drosophila, the three mammalian FUBP proteins are represented by one ortholog, Psi. We have taken advantage of this reduced functional redundancy to demonstrate that an essential in vivo function of Psi is control of cell and tissue growth. Analysis of published Co-IP-mass spectrometry screens positioned Psi in an interactome predominantly comprised of RNA Polymerase II transcriptional machinery. Of great interest was the interaction with most subunits of the transcriptional Mediator (MED) complex, a known sensor of developmental signaling inputs. Moreover, manipulation of MED activity modified Psi-dependent growth, which suggests that Psi interacts with the MED complex to integrate developmental growth signals with transcription of growth regulators. Our work indicates that a key target of the Psi/MED network that impacts tissue growth is the MYC transcription factor. Further to this, transcriptome-wide expression analysis comparing Psi and MYC depleted wing imaginal discs suggests that in addition to MYC-dependent targets, Psi regulates expression of RNA processing machinery. Our future studies are directed towards identifying direct transcriptional targets of Psi.